Effects of second phase particles on the tensile deformation and fracture behavior of the commercial 5083 aluminum alloy plates at -196°C and at room temperature were discussed.
According to the results, the initiation of the voids in the process of tensile deformation and fracture, three types of behavior were observed, such as, (a) initiation of void due to separation of the interface between the second phase particles and matrix phase, (b) fracture of second phase particles, (c) separation of the grain boundary.
It appeared that such voids as initiated from rectangular form particles of Al₆(Fe, Mn) tended to positively grow to the crack formation and propagation.
Occurrence rate of fracture of second phase particles was increased with the increase of plastic strain. The maximum ratio of fracture of second phase particles to the plastic strain was observed in the tensile deformation at -100°C and slightly decreased at 0°C. The lowest ratio of fracture of the particles was observed at -196°C.

View full abstract

Fatigue tests under alternate bending stress in air and argon gas were carried out for the notched sheet specimens of AZ31 magnesium alloy at temperatures from room tcmperature to 150°C. The fatigue strength at 150°C is some three-fifths as much as that at room temperature. This lowering in fatigue strength well corresponds to that in tensile strength. Within the above test temperature, the relation between σ/σ_B and N_f is described approximately on a same curve. Also, the relation between crack propagation, rate and stress intensity factor in the steady stage of crack propagation is represented nearly by a same line on both logarithmic scales, though it depends somewhat on temperature. The fracture mode is predominantly transgranular cracking but in the early stage of crack propagation intergranular cracks become to appear at 150°C. No clear defference between the results obtained in air and argon gas is observed.

View full abstract

To study the effect of alternating electromagnetic force on the refinement of as-cast aluminum grain structures, both direct magnetic flux and alternating electric current of 0 to 45 kHz were acted on the solidifing aluminum melts. The grain structures were significantly refined under the very low frequency range below 10 Hz in which it was expected that the fluid flow occured in the melt. A little grain refinement effect, however, was observed within the frequency range above 10 Hz in which the vibration was generated in the melt. Further, it was found that the grain refinement effect by the vibration was achieved by nonstationary wave, not by the action of stationary ones.

View full abstract

Molten chlorides such as potassium chloride, sodium chloride and aluminium chloride are used as fluxes for the purification treatment of scrap aluminium. In order to clarify the reactivity of aluminium alloy melts with these molten salts, the dissolution behaviors of Al-4.7wt%Mg and Al-6.04wt%Zn alloys in KCl-NaCl binary melt and KCl-NaCl-AlCl₃ ternary melt have been investigated by the equilibrium experiment conducted with various temperatures and compositions of molten salt. The dissolution reaction of magnesium in KCl-NaCl binary melt greatly proceeded with an increase in temperature, but at high temperatures, this reaction was retained with raising temperature. The changes of these dissolution behaviors may be attributed to the dissolution of aluminium in alloy, which was remarkably accelerated at temeperatures above 760°C. The dissolution reaction of zinc in KCl-NaCl-AlCl₃ ternary melt increased with increases in temperture and content of aluminium chloride. In this system, aluminium in alloy dissolves significantly by the disproportionation reaction even in molten salt of low aluminium chloride concentration. Distribution coefficient of magnesium was enlarged with increasing temperature, and at high temperatures, it showed a maximum value at a given temperature depending on the content of sodium chloride in KCl-NaCl binary melt. Distribution coefficient of zinc was enlarged as the temperature and the content of aluminium chloride in KCl-NaCl-AlCl₃ ternary melt increased.

View full abstract

The mechanism of localized corrosion behavior for aluminum vacuum brazing T-joints has been investigated by means of a potentiostat etc. Specimens were prepared from brazing sheet which was made of A3003 (core) and Al-6.6%Si-1.97%Mg-0.18%Fe alloy (filler metal), and A1100 (base metal). The measurement of corrosion potentials and polarization curves were carried out for three positions on specimen. It has been found that base metal is less noble than filler metal, and the limiting diffusion current of dissolved oxygen for position 2, interface of base metal and filler metal, is the largest. From the result of surface observation by using scanning electron microscopy and electron probe micro analyser, it has been found that iron and silicon segrigate on the filler metal side of the interface. The result of dipping test showed that pitting corrosion occured at the interface of base metal and filler metal. Pitting corrosion of the aluminum vacuum brazing T-joints results from galvanic corrosion of base metal and segrigated iron on the filler metal.

View full abstract